The working mode of hysteresis clutches or hysteresis brakes generally depends on poles that provides a magnetic effect in synchronous running or reverse magnetism of a permanent magnetic materials in a slip operation, wherein the slip capacity is converted to heat. In particular, hysteresis brakes are suited for use as retarders in the processing of material in a production plane, e.g. cables, yarn manufacture, coil winding, etc. The system defines the speed at which the material is removed from the cycle, the retarder defining the traction. For this purpose, the material is adequately led out of the supply via a roller, e.g. by the material winding around the latter, wherein the roller transmits to the material the braking action of the hysteresis brake.
The reverse magnetization in the hysteresis ring made of semihard magnetic permanent magnetic material (sic) can be implemented by different arrangements of exciter magnets. German Patent 28 21 973 thus describes a magnetic torque clutch essentially consisting of the combination of a permanent-magnet excited eddy current clutch. Said known clutch or brake has a driving clutch body on the front side of which a flat hysteresis ring is situated. Opposite to said hysteresis ring, at adequate distance, several permanent magnets are provided in annular arrangement, the south-north alignment changing in the curve of the ring. The permanent magnets are situated on the front surface of a magnetizable disc. In this known arrangement, there is no possible adjustability of the torque.
DE-OS 37 32 766 has disclosed a permanent-magnet excited hysteresis clutch or brake with a hysteresis part designed as a bell-shaped rotor and having an exciter part consisting of an inner and an outer pole ring, wherein the magnetic poles are disposed without contact at both sides of the bell-shaped rotor; the pole rings consist of a soft magnetic material in which are located permanent magnetic pieces which are fully embedded in the soft magnetic material so that the magnetic poles facing the bell-shaped rotor are alternately formed of a permanent magnet and a soft magnet; the outer pole ring and the inner pole ring are rigidly interconnected but magnetically separated by a non-magnetizable intermediate ring.
With such a hysteresis brake, a simple design is not only achieved but also an adjustability of the torque to be transmitted due to the axial depth of immersion of the hysteresis ring body is changeable. In this known hysteresis brake, this results from an arrangement of the hysteresis ring body on a threaded spindle and fixing the position of the ring on the spindle, e.g. by a fixed nut. The torque is thus continuously changed, but in this known hysteresis brake, it is a disadvantage also that the two annular air gaps are required due to the magnet poles situated on both sides of the bell-shaped rotor and that costly processing in the form of a groove milling for embedding the permanent magnet pieces in the pole rings is required. Finally, in this known solution, it is disadvantageous that the braking torque is transmitted by the regulating device and, therefore, the fixed nut is required which at each adjusting operation has to be time-consumingly first loosened and then retightened.
The problem to be solved by this invention is to provide a simplified hysteresis brake with contactless torque transmission of a speed-independent torque which is quickly is manually adjustable as to its braking torque in very small steps which makes possible an exact reproducibility of the adjustment and ensures the uniformity of the adjustment even in case of a large number of specimens.